Ebp2p is essential for the assembly of 60S ribosomal subunits, and it interacts with other ribosome assembly factors in Saccharomyces cerevisiae. Two-hybrid screening exhibited that Ebp2p interacted with a small ubiquitin-related modifier (SUMO)-ligase Siz2p and SUMO-related proteins, Ris1p and Wss1p. Mutations of SUMO attachment sites of Ebp2p led to significantly weak interactions with Siz2p, Wss1p, and Ris1p, whereas they exhibited positive interactions with ribosome assembly factors. A SUMO-binding motif of Ris1p was required for interaction with Ebp2p. These results suggest that SUMO mediates the interaction between Ebp2p and SUMO related proteins and that Ebp2p switches its interaction partners via sumoylation.